Indoor behavior and risk assessment following space spraying of d-tetramethrin and d-resmethrin

To clarify the indoor behavior of insecticides in space spraying, an aerosol canister (containing a mixture of 0.45 g d-tetramethrin and 0.06 g d-resmethrin in a 300-mL product) was applied to a typical Japanese room under various conditions and temporal concentrations in air; floor, walls, and ceiling were monitored. Air concentrations were chiefly dependent on ventilation rates but not on air circulation by an air conditioner. During a periodic spraying, the airborne insecticides did not accumulate in the room, but the floor residues gradually increased with the number of sprayings. After cessation of spraying, however, dislodgeable residues on the floor decreased with time. The time-dependent behavior of d-tetramethrin was simulated by a mathematical model (InPest) developed by the authors, and it was found that the estimated values agreed fully with actually measured values. The simulation model also clarified the amount of insecticide evaporated from the room material, the amount vented to the outdoors, and so on. Indoor exposure levels of d-tetramethrin and d-resmethrin to the room's occupants were estimated with the monitored concentrations when a 10-sec spraying was done twice a day for 30 days. The margins of safety, which were obtained by dividing the no observed effect levels by the exposure levels, were over 100 for unclothed occupants, even in the room with the windows closed.